Ankle prosthesis for the arthrodesis of the calcaneum

ABSTRACT

A prosthetic ankle assembly including an astragalar component with an upper articular surface that forms part of an ankle joint prosthesis and a lower surface with a shape adapted to engage an upper face of an astragalus. An astragalocalcanean rod is positioned in an astragalocalcanean channel extending from the lower face of the calcaneus to the upper surface of the astragalus. A first end of the astragalocalcanean rod is engage with the lower surface of the astragalar component and a second end of the astragalocalcanean rod is engaged with a lower region of the calcaneus. A distance between the second end of the astragalocalcanean rod is adjustable relative to the lower surface of the astragalar component to adjustably compress the calcaneus against the astragalus.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to prior French Application No.06 09001, filed Oct. 13, 2006, entitled ANKLE PROSTHESIS FOR THEARTHRODESIS OF THE CALCANEUM.

FIELD OF THE INVENTION

The present invention relates to a prosthetic ankle assembly and to asurgical method for implanting such an assembly, and in particular, tothe treatment of an ankle in which the articulation between theastragalus and the calcaneus are damaged.

BACKGROUND OF THE INVENTION

One possible treatment involves fusing the three bones represented bythe calcaneus, astragalus and tibia, as is proposed inUS-A-2005/0107791. A long compression screw internally connects thetibia and the calcaneus by passing through the astragalus, in such a wayas to block these three bones relative to one another. This results in aconsiderable loss of mobility for the patient, since the ankle istotally blocked.

Another possible treatment involves fusing the calcaneus and astragalus,with the aid of a dedicated arthrodesis rod and re-establishing thearticular capacity between the astragalus and tibia, by implanting anankle joint prosthesis. However, the two articulations then have to betreated in two stages: the arthrodesis of the calcaneus and astragalusrequires a consolidation period of at least six months, which delays theimplantation of the articular prosthesis between the astragalus and thetibia.

US-A-2005/0288792 discloses an astragalar component of an ankle jointprosthesis with which it is possible to re-establish the articularcapacity between the astragalus and the tibia, while at the same timeusing an astragalocalcanean rod that extends from a lower side of theastragalar component to the upper part of the calcaneus, in so doingpassing right through the astragalus. In one embodiment, the upper endof this rod is screwed directly into internal threads of the astragalarcomponent, which threads open out on the lower side of this component.Before being implanted, the component and the rod are firmly immobilizedrelative to each other by screwing. When this screwed assembly isimplanted, the rod guarantees good anchoring of the astragalarcomponent, since the latter is thus fixed both to the astragalus andalso to the upper part of the calcaneus, which explains why theprosthetic assembly is more specifically intended for revision of anarthroplasty of the ankle. However, the assembly does not effectivelyblock the articulation between the calcaneus and the astragalus, sincerelative movements around and/or along the rod remain possible and, inpractice, appear quickly.

FR-A-2 220 235 proposes a prosthetic ankle assembly comprising anastragalar component of an ankle joint prosthesis in the form of asupport designed to be fixed to the astragalus of a patient. Thissupport is intended to cooperate in an articulated manner with a tibialrod, with interposition of an intermediate articulated component. In itslower part, the astragalar support is joined to three anchoring feet,namely two anterior feet and one posterior foot, which are intendedrespectively to be inserted into corresponding cavities formed in theastragalus and in the calcaneus. As regards the posterior foot, oneembodiment entails this foot being formed by at least one sagittal screwthat passes through the support from top to bottom, until bearing withits head on the support, while its stem is inserted, without beingscrewed, into the cavity of the calcaneus, plugged with cement. Thebenefit of using such a screw is that, if necessary, it can be unscrewedin order to facilitate the removal of the support. Thus, the posteriorfoot of this prosthetic assembly provides a stable means of bearing onthe calcaneus, but, even in the form of a screw inserted into cement,this foot does not totally block the articulation between the astragalusand the calcaneus in an effective manner.

WO-A-01/30264 and US-A-2005/124995 for their part disclose a prostheticankle assembly comprising an astragalocalcanean rod that is introducedinto a cavity formed beforehand through the astragalus and in the upperpart of the calcaneus. This rod is used to anchor an astragalar plate,which is fitted in place and fixed to the astragalocalcanean rod afterthe rod has been placed in the aforementioned bone cavity. Hence, thisrod does not provide any effective blocking of the articulation betweenthe calcaneus and the astragalus so that, in order to limit the relativemovements between these two bones, additional screws are fitted betweenthe astragalar plate and the astragalocalcanean rod, in order tostabilize the position of the latter.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a method and apparatus that blocksthe articulation between the calcaneus and the astragalus and tore-establish an articular capacity between the astragalus and the tibiaof a patient, all in a single intervention.

To this end, the subject matter of the invention is a prosthetic ankleassembly, comprising an astragalar component which forms part of anankle joint prosthesis and which is designed to be fixed to theastragalus of a patient. An astragalocalcanean rod of which a firstlongitudinal end is designed to be fixed to the astragalar component, byits shape complementing that of a dedicated part of the astragalarcomponent. The dedicated part is provided on a lower side of thiscomponent intended to be directed towards an upper face of theastragalus. The astragalocalcanean rod is equipped, at its secondlongitudinal end, with an engagement feature for osseous engagement ofthe calcaneus of the patient, so as to approximate and thereby compressthe calcaneus against the astragalus when the first end of the rod isfixed to the dedicated part of the astragalar component.

When the prosthetic assembly according to the invention is implanted,its astragalar component permits articular movements between theastragalus and the tibia of a patient, especially by being connected toa prosthetic tibial component fixed to the tibia, and to a prostheticbearing interposed between the astragalar and tibial components. On theother hand, the astragalocalcanean rod blocks the articulation betweenthe calcaneus and the astragalus, by these two bones being compressedagainst each other. In practice, this bone compression is obtained byfixing the first end of the rod in the astragalar component, whichengages the second end of the rod directly with the calcaneus. For thispurpose, a fixation means and the engagement means provided respectivelyat the ends of the rod are structurally configured to obtain aprogressive compression effect between the calcaneus and the astragalusas the second end of the rod advances into the calcaneus, whilst thefirst end is coupled to the dedicated part of the astragalar componentresting on the astragalus.

In practice, the rod is introduced from a lower face of the calcaneusinto an astragalocalcanean channel that has been drilled beforehandthrough the calcaneus and the astragalus and that opens out on thededicated part of the astragalar component when the latter is placed onan upper face of the astragalus. Thus, advantageously in a singlesurgical intervention, the astragalar component and theastragalocalcanean rod are implanted by being coupled to each otherduring the intervention, while the rod passes right through thecalcaneus and the astragalus, in order to compress them and therebyimmobilize them against each other. In other words, the operation ofarthroplasty between the astragalus and the tibia and the operation ofarthroplasty between the astragalus and the calcaneus are performedduring the same surgical intervention, which limits the surgical risksfaced by the patient and which allows the surgeon to use the samesurgical routes for the two operations.

In addition, the astragalocalcanean rod ensures immobilization of theastragalar component relative to the astragalus and to the calcaneus,which improves the fit of the astragalar component. Moreover, in theevent of revision of the prosthetic assembly according to the invention,the bearing action on the calcaneus is safe and reliable in the sensethat this bone is firmly fused to the astragalus.

According to other advantageous characteristics of this prosthetic ankleassembly, taken either singly or in all the technically possiblecombinations:

-   the astragalocalcanean rod is designed to extend in length from the    upper face of the astragalus, on which the astragalar component is    fixed, as far as a lower face of the calcaneus directed away from    the astragalus;-   the engagement means comprises an external thread designed to engage    in the bone substance of the calcaneus when the first end of the    astragalocalcanean rod is fixed in the dedicated part of the    astragalar component;-   the engagement means comprises a ring, fixedly or moveably    surrounding the second end of the astragalocalcanean rod and adapted    to be pressed against a lower face of the calcaneus, opposite to the    astragalus, when the first end of the rod is fixed to the dedicated    part of the astragalar component;-   the engagement means for engaging the calcaneus has a maximum    transverse dimension strictly greater than the maximum transverse    dimension of a fixation means for fixing the first end of the    astragalocalcanean rod to the astragalar component;-   either the first end of the astragalocalcanean rod or the dedicated    part of the astragalar component is equipped with an external    thread, while the other of them forms a substantially complementary    internal thread;-   the astragalar component is equipped, on its lower side, with an    anchoring means for osseous anchoring in the astragalus, inside of    which anchoring means the dedicated part is arranged;-   the anchoring means includes a hollow stub in which the external    thread or internal thread of the astragalar component is delimited,    preferably in a manner substantially coaxial to the rest of the    stub;-   the astragalocalcanean rod is equipped, at its second longitudinal    end, with a driving profile, preferably driven in rotation on    itself, designed to cooperate with a tool for coupling the rod to    the astragalar component;-   the profile or another profile for driving the rod is designed to    cooperate with a tool for disconnection between the rod and the    astragalar component;-   the assembly also comprises a tibial component of an ankle joint    prosthesis, designed to be fixed to the tibia of the patient, and a    prosthetic bearing designed to be interposed between the astragalar    component and tibial component.

The invention also relates to a surgical method for implanting aprosthetic ankle assembly, the assembly comprising an astragalarcomponent of an ankle joint prosthesis, and an astragalocalcanean rod ofwhich a first of its two longitudinal ends is designed to be fixed tothe astragalar component, by its shape complementing that of a dedicatedpart of the component, and of which the second longitudinal end isequipped with an engagement means of osseous engagement. The method ofimplantation comprising steps of:

-   -   preparing an upper face of an astragalus to receive an        astragalar component;    -   forming an astragalocalcanean channel between an the upper face        of the astragalus and a lower face of a calcaneus;    -   locating the astragalar component on the upper face of the        astragalus;    -   inserting an astragalocalcanean rod into the astragalocalcanean        channel from the lower face of the calcaneus;    -   engaging a first end of the astragalo-calanean rod with the        astragalar component and a second end of the astragalo-calanean        rod with a lower region of the calcaneus; and    -   adjusting a distance between the second end of the        astragalocalcanean rod relative to a lower surface of the        astragalar component to adjustably compresses the calcaneus        against the astragalus.

This method makes it possible, in a single surgical intervention, toimplant a prosthetic ankle assembly of the kind defined above, in orderto permit arthrodesis of the calcaneus and astragalus and, at the sametime, arthroplasty between the astragalus and the tibia of a patient.Arthrodesis refers to a surgical fixation of a joint, ultimatelyresulting in bone fusion. Basically, the procedure is artificiallyinduced ankylosis performed to relieve pain or provide support in adiseased or injured joint.

According to an advantageous embodiment of this method, during step i),a substantially cylindrical recess is hollowed out in the upper face ofthe astragalus in order to receive a hollow bone-anchoring stub which isprovided on the astragalar component and in which the dedicated part isarranged, and, during step ii), the astragalocalcanean channel isdrilled from the upper face of the astragalus, in a continuation of therecess.

In this case, to make matters easier, a drill bushing is used to drillthe astragalocalcanean channel, by resting this bushing in the recessformed during step i).

Advantageously, in order to promote the fusion of the calcaneus and theastragalus, the method comprises, before step ii), an additionalsurgical step during which bone substance is inserted between theastragalus and the calcaneus by arthroscopy.

Moreover, after consolidation of the arthrodesis of the calcaneus andastragalus, the method advantageously comprises a postoperative step inwhich the astragalocalcanean rod is withdrawn by disconnecting its firstend from the dedicated part of the astragalar component.

BRIEF DESCRIPTIONS OF THE SEVERAL VIEWS OF THE DRAWING

The invention can be better understood on reading the followingdescription given purely by way of example and made with reference tothe drawings, in which:

FIG. 1 is a front view, in partial cross section, of a prosthetic ankleassembly implanted in the left ankle of a patient in accordance with anembodiment of the present invention;

FIG. 2 is an exploded side view, according to the arrow II indicated inFIG. 1, of part of the prosthetic assembly, depicted without the bonesof the ankle;

FIGS. 3A and 3B are schematic cross sections, along the line III-III inFIG. 1, illustrating two successive steps in the implantation of theprosthetic assembly; and

FIG. 4 is a view similar to FIG. 3B, illustrating a variant of theprosthetic ankle assembly in accordance with an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows schematically the lower ends of a tibia T and of a peronealbone P or fibula of a human being, and also the corresponding astragalusA and calcaneus C, thereby illustrating the constituent bones of theleft ankle of a patient. FIG. 1 also shows a prosthetic ankle assembly 1comprising four separate components implanted in the ankle of thepatient, namely a tibial component 10, an astragalar component 20, aprosthetic bearing 30, interposed between the tibial and astragalarcomponents, and an astragalocalcanean rod 40. In FIG. 1, only thebearing 30 is shown in frontal section, whereas the broken lines areused to symbolize the contours of the components concealed by bonesubstance.

For convenience, the description that follows relates to the bones ofthe ankle in their anatomical position, that is to say the terms“posterior” or “rear”, “anterior” or “front”, “upper”, “lower”, etc.,are to be understood in relation to the ankle of the patient whenstanding upright on a substantially horizontal surface.

The tibial component 10 comprises a plate 11 which is attached in afixed manner to the lower end of the tibia T. For this purpose, theplate 11, on its upper face 11A, is joined, via a sagittal fin 12, to ahollow bone-anchoring stub 13. Additional and/or alternative means foranchoring the plate 11 are conceivable, provided that they effectivelyimmobilize the tibial component at the lower end of the tibia T.

On its lower side, the plate 11 delimits a plane surface 11B intended toform a sliding support for the plane upper surface 30A of the bearing30.

The astragalar component 20 comprises a main block 21 attached in afixed manner to the upper end of the astragalus A. For this purpose, theblock 21 is made integral with a hollow bone-anchoring stub 22 thatextends downwards from the lower side 21B of the block 21, as isrepresented by broken lines in FIG. 1 and as can be clearly seen in FIG.2.

On its upper side, the block 21 delimits an articular surface 21Aintended to cooperate with a matching articular surface 30B delimited bythe lower side of the bearing 30. In sagittal section, the surface 21Ahas an arched profile, with its concavity directed downwards, as can beseen in FIG. 2. The articular surfaces 21A and 30B are thus designed toslide against each other along this curved profile, in what is anessentially antero-posterior direction. Advantageously, these surfaces21A and 30B between them permit a medio-lateral clearance, whichcombines with the curved movement of sliding in the antero-posteriordirection.

As is shown in FIG. 2, the rod 40 extends lengthwise about a completelyvertical central axis X-X. This rod comprises, in succession along itslength, a first threaded end 41, an externally smooth and regular part42, and a second threaded end 43. The end 41, the regular part 42 andthe end 43 are successively of increasing size, such that, on the onehand, the maximum diameter d₄₁ of the external thread 41A of the end 41,that is to say the maximum transverse dimension of this end 41 in thearea of the crest of the thread, is less than or equal to the externaldiameter of the part 42, and, on the other hand, the maximum diameterd₄₃ of the external thread 43A of the end 43, that is to say the maximumtransverse dimension of this end 43 at the crest of the thread 43A, isstrictly greater than the diameter of the regular part 42.

The external thread 41A of the end 41 is designed to be received byscrewing into a complementary internal thread 22A which, as is indicatedby broken lines in FIG. 2, is delimited by the inner face of the hollowstub 22 and is preferably centred on the central longitudinal axis ofthis stub.

At its end 43, the rod 40 delimits a recess 44 which is substantiallycentred on the axis X-X and opens out axially downwards to the outside,as is indicated by broken lines in FIG. 2. This recess 44 has atransverse profile 44A, for example of square shape, intended tocooperate with a complementary tool for driving the rod 40 in rotationon itself about the axis X-X.

A surgical method for implanting the prosthetic ankle assembly 1 willnow be described.

In a first step, the bones of the patient's ankle have to be prepared.For this purpose, the surgeon uses cutting means (not shown) in such away as to, on the one hand, resect the lower end of the tibia T and forma substantially plane surface T₁, and, on the other hand, resect theupper end of the astragalus A and form a multi-facet surface A₁comprising two main surfaces which are inclined relative to each other,as can be seen in FIG. 3A. In the face A₁, a cylindrical recess A₂,indicated by broken lines in FIG. 3A, is hollowed out in an overallvertical direction, for example by means of a milling cutter. Thisrecess A₂ thus defines a central longitudinal axis A₃.

At this stage of the surgical intervention, the upper face A₁ of theastragalus A is in a configuration suitable for receiving the astragalarcomponent 20, it being understood that the recess A₂ is madesubstantially complementary to the stub 22 in order to anchor thiscomponent 20 on the astragalus. However, before fitting the astragalarcomponent 20 in place, the surgeon drills through the astragalus A andcalcaneus C, from the upper face A₁ of the astragalus to a lower face C₁of the calcaneus, in such a way as to form an astragalocalcanean channelAC indicated by broken lines in FIG. 3A. This channel AC is drilled in arectilinear continuation of the recess A₂, by being substantiallycentred on the axis A₃. To do this, the surgeon advantageously uses adrill bushing 50, indicated partially and schematically in FIG. 3A. Thisbushing 50 has a tubular shape designed to be received in asubstantially complementary manner in the recess A₂, substantiallycoaxial to the recess. In this way, the bushing 50 bears in the recessA₂ in such a way as to guide the introduction and advance of a drill bitsuccessively through the astragalus and the calcaneus, as is indicatedby the arrow 51 in FIG. 3A. The surgeon thus drills theastragalocalcanean channel AC rapidly and with precision, usingancillary equipment traditional in the field of orthopaedic surgery.

After the astragalocalcanean channel AC has been drilled, the surgeonplaces the astragalar component 20 on the upper face A₁ of theastragalus A and places the astragalocalcanean rod 40 in the channel AC.More precisely, the rod 40 is introduced into the channel AC from thelower face C₁ of the calcaneus, with its end 41 directed upwards. Theinternal diameter of the channel AC is made substantially equal to theexternal diameter of the regular part 42, such that the rod is easilyadvanced through the channel in an upward translational movement andparallel to the axis A₃, until the end 41 reaches the point where thechannel AC opens into the recess A₂. As this recess is occupied by thestub 22, advancing the rod 40 requires the latter to be driven inrotation on itself about the axis X-X, in such a way as to screw theexternal thread 41A into the internal thread 22A, as is indicated by thearrow 60. In practice, the rod is driven in rotation by means of a toolwhose head, indicated only by broken lines and reference number 61 inFIG. 3B, is engaged with the profile 44A in the recess 44.

It will be understood that, by giving the rod 40 a suitable lengthwisedimension, the screwing of the end 41 into the stub 22 is accompanied bythe screwing of the end 43 into the calcaneus, the external thread 43Aengaging directly in the bone substance of the calcaneus at the pointwhere the channel AC opens out on the lower face C₁ of the calcaneus. Inother words, the rod 40 has a length substantially equal to that of theastragalocalcanean channel AC, such that the rod can extend through theastragalus and the calcaneus with its end 41 in the area of the upperface A₁ of the astragalus and with its end 43 in the area of the lowerface C₁ of the calcaneus.

The twin screwing of the external threads 41A and 43A causes theastragalus A and the calcaneus C to be gradually approximated to eachother, thereby compressing these two bones against each other in thearea of their respective contacting surfaces. It will be appreciatedthat the structural features of these external threads, in particulartheir respective pitch, are chosen so as to achieve compression valuesthat are sufficient to efficiently block the astragalus and thecalcaneus against each other, without generating excessive stress in thebones.

The other components of the prosthetic assembly 1 are implanted inparallel with this. The tibial component 10 is attached and immobilizedon the lower end of the tibia T, with its plate 11 resting flat againstthe face T₁, then the prosthetic bearing 30 is attached between thecomponents 10 and 20. The assembly 1 is then in the implantationconfiguration illustrated in FIG. 1 and the surgical intervention isconcluded.

After consolidation of the arthrodesis between the astragalus A and thecalcaneus C, which generally takes between six and twelve months, theastragalocalcanean rod 40 can be withdrawn by unscrewing its ends 41 and43. The surgeon then advantageously uses the profile 44A by introducinga suitable disconnecting tool into the latter. To promote and acceleratethis arthrodesis, bone substance can advantageously be inserted betweenthe astragalus and the calcaneus before implantation of the prostheticassembly 1. Before jointly drilling right through the astragalus A andthe calcaneus C, an arthroscope is inserted into the junction areabetween the astragalus and the calcaneus in order to place bonesubstance there.

FIG. 4 shows a variant of the astragalocalcanean rod 40, which differsfrom the embodiment considered in FIGS. 1 to 3B only at its lower end43. The external thread 43A is cancelled, so that the external surfaceof the end 43 is smooth and extends in the straight continuation of theexternal surface of the regular part 42, except at its end area thatforms a bulge 43B radially protruding externally from the rest of thissurface. Unlike the embodiment of FIGS. 1 to 3B, the end 43 of the rod40 of FIG. 4 is associated with a ring 45 externally surrounding thisend. This ring has an internal diameter that is both substantially equalor greater than the external diameter of end 43, except at its end bulge43B, and lower than the maximum external diameter of this bulge. Inpractice, the ring 45 is pulled around the rod 40 by being introducedfrom upper end 41 while the rod is still not introduced into theastragalocalcanean channel AC.

When the external thread 41A of the end 41 of the rod 40 is screwed intointernal thread 22A of the astragalar component 20, by driving inrotation the rod by means of the tool whose head is engaged within therecess 44, the ring 45 is thus interposed between the lower face C₁ ofthe calcaneus C and the end bulge 43B of the rod until this bulge drivesthe ring 45 in a pressed contact against the face C₁ of the calcaneus.Thus, the ring 45 transmits and distributes the clamping stress on theface C₁ of the calcaneus, in the same way as a washer. The calcaneus isthus compressed against the astragalus A, until to efficiently block theastragalus and the calcaneus against each other.

A radial clearance between the internal face of the ring 45 and theexternal face of the end 43, above its end bulge 43B, allows adjustmentof the position of the ring with respect to the rod during its pressingagainst the calcaneus C. Thus, this relative mobility between the ringand the end 43 compensates for a potential misalignment between thecentral axis of the ring and the axis X-X of the rod.

According to a not shown variant, the ring 45 is fixedly secured at thelower end 43 of the rod 40, for example being directly integral with therod. In this case, in order to increase the pressing surface of thisfixed ring against the lower face C₁ of the calcaneus C during thescrewing of the external thread 41A into the astragalar component 20,this calcanean face C₁ is, if necessary, beforehand wrought, so that asubstantially plane surface, inscribed in a plane substantiallyperpendicular to the axis A₃ of the astragalocalcanean channel AC, isdelimitated around the point where this channel opens into the recessA₂.

Configurations other than the external thread 43A and the ring 45 can beprovided at the lower end 43 of the astragalocalcanean rod 40 in orderto engage the calcaneus C and compress it against the astragalus A whenscrewing the upper end 41 into the astragalar component 20. For example,the lower end 43 can have an outer surface in the shape of a truncatedcone or flare widening towards the bottom.

Other variations on the prosthetic ankle assembly 1 and on theimplantation method that have been described above are also conceivable.By way of example:

The central axis of the internal thread 22A can be offset from thecentral axis of the stub 22, the drill bushing 50 then being providedwith a similar offset in order to drill the astragalocalcanean channelAC in the possibly inclined continuation of the recess A₂;

The structure of internal thread 22A and external thread 41 A can bereversed, such that the end 41 of the rod 40 forms an internal threadthat can be screwed around an external thread formed in the stub 22, forexample delimited by a central pin internal to this stub; moregenerally, other types of means permitting coupling throughcomplementary shapes between the upper end of the rod 40 and the lowerside 21B of the astragalar component 20 are conceivable, provided thatthese means lead to engagement of the lower end of the rod with thecalcaneus C in order to compress the latter against the astragalus A;thus, a coupling by means of a bayonet structure is possible, and alsocoupling structures with stressing obtained exclusively throughrectilinear translation;

By virtue of the fact that they bear slidingly on each other at theirsurfaces 11A and 30A, the tibial component 10 and the bearing 30 aremovable relative to each other, which generally leads the ankleprosthesis comprising the elements 10, 20 and 30 to be designated as aprosthesis with a “movable bearing”; however, the astragalar component20 can alternatively be joined to a “fixed” bearing, that is to say abearing placed fixedly against a tibial component;

The astragalar component 20 and the astragalocalcanean rod 40 are notnecessarily to be used jointly with a tibial component and a prostheticbearing such as the elements 10 and 30; the astragalar component can infact be made to cooperate in an articulated manner directly with thelower anatomical end of the tibia T if the latter has sufficientarticular capacity; the prosthetic ankle assembly can then be designatedas a partial prosthetic assembly, whereas the prosthetic assembly 1 inFIG. 1 is to be considered as a total prosthetic assembly; and/or

If necessary, the fixation of the astragalar component 20 to theastragalus A can be strengthened by additional means.

Patents and patent applications disclosed herein, including those citedin the Background of the Invention, are hereby incorporated byreference. Other embodiments of the invention are possible. It is to beunderstood that the above description is intended to be illustrative,and not restrictive. Many other embodiments will be apparent to those ofskill in the art upon reviewing the above description. The scope of theinvention should, therefore, be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled.

1.-14. (canceled)
 15. Surgical method for implanting a prosthetic ankleassembly comprising the steps of: preparing an upper face of anastragalus of an ankle to engage a lower surface of an astragalarcomponent; forming an astragalocalcanean bore extending completelythrough the astragalus and a calcaneus of the ankle between the upperface of the astragalus and a lower face of the calcaneus; locating theastragalar component on the upper face of the astragalus so that thelower surface of the astragalar component engages the upper face of theastragalus and an upper articular surface of the astragalar componentforms part of an ankle joint prosthesis; inserting an astragalocalcaneanrod into the astragalocalcanean bore through the lower face of thecalcaneus; and coupling a first end of the astragalocalcanean rod to thelower surface of the astragalar component so that a second end of theastragalocalcanean rod approximates and engages the lower region face ofthe calcaneus so as to progressively compress the calcaneus against theastragalus for performing an arthrodesis between the calcaneus and theastragalus.
 16. The method of claim 15 wherein the step of locating theastragalar component on the upper face of the astragalus includesreceiving an anchor structure of the lower surface of the astragalarcomponent in the astragalocalcanean bore.
 17. The method of claim 16wherein the step coupling the first end of the astragalocalcanean rodwith to the lower surface of the astragalar component includes screwingthreads of the first end of the astragalocalcanean rod to complementarythreads of the anchor structure.
 18. The method of claim 15 wherein thestep of coupling the first end of the astragalocalcanean rod to thelower surface of the astragalar component includes screwing threads ofthe first end of the astragalocalcanean rod to complementary threads ofthe lower surface of the astragalar component.
 19. The method of claim15 wherein when coupling the first end of the astragalocalcanean rod tothe astragalar component, a ring of the second end of theastragalocalcanean rod is pressed against the lower face of thecalcaneus.
 20. The method of claim 15 wherein the first and second endsof the astragalocalcanean rod are linked to each other by a smoothintermediate part, the second end of the astragalocalcanean rodcomprising a diameter greater than a diameter of the intermediate part,and wherein when coupling the first end of the astragalocalcanean rod tothe astragalar component, the diameter of second end of theastragalocalcanean rod engages the lower face of the calcaneus.
 21. Themethod of claim 15 comprising removing the astragalocalcanean rod fromthe astragalocalcanean bore through the lower face of the calcaneusafter fusion of the astragalar with the calcaneus.
 22. The method ofclaim 15 comprising the steps of: implanting a tibial component of anankle joint prosthesis in a distal end of a tibia; and interposing aprosthetic bearing between the astragalar component and the tibialcomponent.
 23. The method of claim 22 wherein the prosthetic bearing isselected from a fixed bearing or a moveable bearing.
 24. The method ofclaim 15 comprising arthroscopically locating a bone substance betweenthe astragalus and the calcaneus.
 25. The method of claim 15 whereinwhen coupling the first end of the astragalocalcanean rod to theastragalar component, threads of the second end of theastragalocalcanean rod are screwed into the lower face of the calcaneus.